1. Field of the Invention
The present invention relates to a lumbar support device which is used in a vehicle seat with a view to adjustably supporting the lumbar part of an occupant on the seat and helping to alleviate the fatigue taken by the occupant from his or her long period of sitting on the seat.
2. 2. Description of the Prior Art
During a long period of driving a vehicle, a fatigue develops from the unchanged seating posture of an occupant on the seat. As a means for alleviating the fatigue, there has been known a lumbar support device for adjustably supporting the lumbar part of the occupant in order for him or her to attain a most comfortable seating state anytime. Generally, most of hitherto lumbar support devices is based on a spring-force adjusting type thereof using a cam having plural discrete cam surfaces. According to this prior art, a lumbar support plate is moved forwardly and backwardly against the lumbar part of the seat under the biasing force of a spring, and the operation of handle fixed to the cam causes rotation of the cam to present a different cam surface level, which expands or contracts the spring to vary its biasing force and thus the lumbar support plate is adjustably moved forwardly and backwardly so as to provide different lumbar support forces to the lumbar part of the occupant on the seat. Thus, the occupant may adjust the lumbar support force as desired to attain a best seating posture.
However, that conventional lumbar support device has been with such drawback that the use of the cam results in only giving a step adjustment and does not offer a fine, stepless adjustment of lumbar support plate, which has not satisfied the delicate tastes of the occupant who wish to enjoy a fine adjustment to achieve a best lumbar support force.